![]() | Home > Technical (L405) > TDv6 with surging idle for about 2 minute after start |
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
Here's the first video.
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
Video with time base slowed down to show the ramping up of fuel rail pressure and its sudden drop. This is the result of how the PCM is commanding the PCV.
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
And finally this is how it behaves if I intentionally loosen the PCV and let a small amount of pressure bleed off all the time from the high pressure side to the low pressure side.
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
Another test I have done is to supply the FRP sensor with 4.6V from a bench power supply instead of the 5V that the PCM supplies it. With the intended goal being to proportionally lower the output voltage hence making the PCM think that the rail pressure is lower than it really is.
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Spridget Member Since: 09 Dec 2023 Location: Northumberland Posts: 188 ![]() ![]() ![]() |
Wow! This is a bit different to a "My car has an annoying squeak" post.
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janpel Member Since: 13 Jun 2022 Location: Harderwijk Posts: 2 ![]() ![]() ![]() |
Hi ss10, not sure if this helps but what i noticed in your write up is the very high pressure of 56 Mpa.
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
I cant imagine it would have a problem like this if the pump was out of time. Whatever happens that causes the PCM to throw a fit happens in the first few hundred milliseconds after starting. But I have gone down the pump timing rabbit hole as well. On a clean scope capture of just the rail pressure I can see each compression stroke of the pumping elements. Pointed by the red arrow below. That coincides with the crosstalk from the injectors opening. The green arrow. You can see this to some extent in the second video above as well.
56 Mpa is under load and not at idle. That is the max pressure the rail can achieve if I leave the PCV not fully torqued down and allow for some pressure to continuously bleed to the low side. Thanks for the replies. Please keep the comments coming. |
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
Correction. The Metering Valve is closed when energized. My understanding of how it worked was incorrect. During my troubleshooting I accidentally left the metering valve disconnected. Was surprised to find that the engine behaved exactly the same way. Energized the metering valve from an external power supply and the car did not start. Fuel was completely cut-off. Took the metering valves I have apart. The valve barrel is made with very high precision. In the picture below the left most barrel is from a counterfeit valve which was on the car when I got it. The middle one is a used one off of a wrecked but running car with TDv6. Right is a new one from the valve for a TDv8. Each barrel has three openings. The picture is that of the smallest opening on all 3. The counterfeit one is junk. I have two of them, they both are the same. ![]() Same picture but with a scale. Each graduation is 1mm. ![]() So I believe my issue is the metering valve. Its an over-fueling issue. Have also looked at the spare parts for the CP4 pump. Doesn't appear to be any differences in the pumping elements from one pump to the other except for the orientation of out nipple. Would someone with a TDv6 be willing to do a test for me. If you disconnect the metering valve and start the car it should start idling the same way mine does. This will throw a code and check engine light so you would have to clear that. Thanks in advance if you take this on. Shahid |
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ss10 Member Since: 05 May 2025 Location: Reston, VA Posts: 18 ![]() ![]() ![]() |
Capture of actual and commanded rail pressures through SDD.
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